1. Technical Field
This invention relates generally to an aircraft-based missile guidance and tracking system, and in particular to a subsystem for digitally computing the roll angle around the line of sight in optics incorporated in such a system, and for adjusting missile guidance signals to compensate for the computed roll angle, about the line of sight.
2. Discussion
A conventional aircraft-based missile guidance and tracking system includes target acquisition optics. An example of such optics is disclosed in U.S. Pat. No. 3,989,947, to Chapman entitled "Telescope Cluster." As disclosed in Chapman, a system operator locates a missile target and positions an image of the target at the intersection of cross hairs incorporated in the optics. After the operator fires the missile, the optics detect a tracking signal emitted by the missile. This tracking signal is then processed by system computers to produce a guidance signal transmitted to the missile to keep the missile on its intended course. Through use of such a system, a missile fired from an aircraft may be directed to its intended target with a high degree of accuracy.
The high degree of accuracy associated with the abovedescribed typical guidance and tracking system is a result in great part to the system's capability of compensating for aircraft movement subsequent to the firing of the missile. As the system receives the missile tracking signal from the system optics, it processes this signal, along with aircraft position data received from aircraft instrumentation. The processed data is then used in the system missile guidance signals, sent from the system to the missile, to compensate for movement of the aircraft from the original aircraft-to-target coordinates, thus keeping the missile on its intended course.
In particular, one critical component that must be compensated for in the missile guidance signals is the roll of the aircraft around a line of sight of the system optics. For instance, once the missile is fired from the aircraft, it maintains the roll attitude of the aircraft at the time of launch, while the aircraft may roll to the right or left around the original line of sight after the missile is fired. Since the missile tracking system senses the missile positioned in aircraft coordinates, this roll must be corrected in order to stabilize the missile and to prevent the missile from deviating from its intended flight path to the target as the gunner maintains the cross hairs on the target as the aircraft moves.
In the past, roll angle compensation mechanisms incorporated in missile guidance and tracking systems have adjusted guidance commands for roll around the line of sight in system optics through use of electromechanical components, such as resolver/servo systems, to compute the roll angle and to correct the guidance signals output to the missile for the computed roll angle. As a result, however, the roll angle compensation mechanisms were relatively heavy and expensive due to the many mechanical components. In addition, the mechanical components often would go out of alignment due to vibration and wear. As a result, the reliability of such electromechanical error compensation mechanisms was limited.
What is needed then is a roll angle correction system which does not exhibit the limitations of previous electromechanical error mechanisms, and which is less expensive to implement than the previous mechanisms.